What the Anesthesiologist Should Know before the Operative Procedure

Strabismus, or abnormal ocular alignment, is one of the most common ocular problems in children affecting almost 5% of the population. Management consists of conservative therapies such as eyeglasses, prisms, eye patches, or exercises, with the majority of cases requiring surgical repair. Surgical repair involves transsection, reinsertion or resection of the involved ocular muscles and depends on the type of abnormal alignment.

1. What is the urgency of the surgery?

What is the risk of delay in order to obtain additional preoperative information?

This surgery is elective. However, if left uncorrected, unilateral strabismus can lead to amblyopia or impaired vision and retinal development can be delayed. Because visual maturation occurs by age 5, correction to realign the deviated eye is usually pursued early in childhood.

2. Preoperative evaluation

Preoperative evaluation should focus on the presence of co-existing disease and its associated pathophysiology and stabilization of their medical treatment. Of specific concern include those patients with potential congenital heart disease (Downs, Goldenhar, Aperts, Cri du Chat, and Turner's syndromes) or difficult airways.

3. What are the implications of co-existing disease on perioperative care?

Special attention should be made to the presence of conditions known to be associated with strabismus as discussed above. Presence of any of these co-existing conditions and their perioperative management should be carefully reviewed.

c. Pulmonary

Airway: Multiple conditions associated with strabismus put this population at risk of difficult intubation. For the most part this is in association with other congenital or craniofacial anomalies including Aperts, Cri du chat, Crouzon's, Down's, Goldenhars, Moebius, and Stickler syndromes.

Lungs: Marfan's syndrome patients can have an increased risk of pneumothorax

d. Renal-GI:

No specific renal or gastrointestinal pathology is associated with strabismus. However, review of systems should be attained for associated problems especially in patients with specific syndrome.

e. Neurologic:

Known neurologic conditions associated with strabismus include cerebral palsy, myelomeningocele, hydrocephalus, brain tumors, and developmental delay. Acute issues involving any of these disorders likely will take precedence over strabismus correction.

f. Endocrine:

Patients with congenital syndromes are often at risk of endocrine disorders as well. Thorough history and physical or review of specific syndrome should help guide further need for endocrine workup. Specifically, attention should be paid to homocystinuria patients who can be at risk for hypoglycemia perioperatively and Turner syndrome patients who have multiple endocrine disorders including diabetes mellitus and hypothyroidism.

g. Additional systems/conditions which may be of concern in a patient undergoing this procedure and are relevant for the anesthetic plan (eg. musculoskeletal in orthopedic procedures, hematologic in a cancer patient)

The anesthesiologist should be aware of other ocular pathology that might alter the surgical and therefore the anesthetic plan.

4. What are the patient's medications and how should they be managed in the perioperative period?

No medications are taken specific to strabismus repair.

h. Are there medications commonly seen in patients undergoing this procedure and for which should there be greater concern?

No.

i. What should be recommended with regard to continuation of medications taken chronically?

Chronic medications for medical conditions should be continued in the perioperative period.

Patients with myelomeningocele can have acquired strabismus. Myelomeningocele is associated with increased incidence of latex allergy and are treated as such.

l. Does the patient have any antibiotic allergies- [Tier 2- Common antibiotic allergies and alternative antibiotics]

N/A

m. Does the patient have a history of allergy to anesthesia?

The use of succinylcholine is associated with a 4-fold increase in risk for masseter muscle rigidity versus the general pediatric population. This has led to an association of increased risk for malignant hyperthermia in this population. All of these patients should specifically be asked about personal and family history of malignant hyperthermia.

Malignant hyperthermia

Documented

Avoid all trigger agents such as succinylcholine and inhalational agents, anesthetic machine should be flushed with oxygen.

Proposed general anesthetic plan: oral premedication with midazolam depending on age of patient, awake IV placement, total IV anesthetic agent.

Insure MH cart available.

5. What laboratory tests should be obtained and has everything been reviewed?

No specific laboratory tests to check in strabismus repair. Otherwise, co-morbid medical conditions should dictate need for laboratory tests. Common laboratory normal values will be same for all procedures, with a difference by age and gender

Intraoperative Management: What are the options for anesthetic management and how to determine the best technique?

Anesthesia for this procedure is general anesthesia. Depending on the age of the child, oral premedication with midazolam (0.5-1 mg/kg) might be warranted. Standard mask induction should be followed by establishment of IV access. Airway may be controlled via flexible LMA or endotracheal tube although an endotracheal tube may be preferable for better control of the airway and ventilation. Nondepolarizing muscle blockade is usually utilized. Regional anesthesia is usually not performed but may be considered.

Many opthamologists request the use of muscle relaxants for adequate performance of a forced duction test to determine paretic versus restrictive disorders. Succinylcholine should be avoided due to prolonged muscle contraction and interference with test interpretation for at least 15 minutes after dosing.

Due to manipulation of the extraocular muscles, the risk of oculocardiac reflex stimulation is very high resulting in bradycardia or other dysrhythmia. Atropine 0.02 mg/kg can be administered before the start of the procedure for prophylaxis.

Regional anesthesia

In a pediatric population, most regional anesthesia is performed under general anesthesia due to difficulty with patient cooperation. As such, the regional anesthetic is mostly for postoperative pain management. Post operative pain for strabismus surgery is generally mild and mostly conjunctival in origin.

Retrobulbar block

Injection in the muscular cone that provides akinesia for extraocular muscles by blockade of CN 2, 3, and 6 as well as sensory blockade for the conjunctiva, cornea and uvea by blocking the ciliary nerves.

Peribulbar block: Injection above and below orbit to block ciliary nerves and CN 3 and 6 without blockade of the optic nerve. It has less potential for intraocular or intradural injection but can have lower rate of complete, dense block.

General anesthesia

Benefits:Strabismus surgery in the pediatric population requires the use of general anesthesia.

Other issues: The incidence of post operative nausea and vomiting is very high in strabismus surgery (40-85%)

Airway concerns: As discussed previously, syndromes associated with strabismus can have associated abnormalities that make intubation or ventilation more difficult.

Monitored anesthesia care

N/A

6. What is the author's preferred method of anesthesia technique and why?

Premedication with oral midazolam if appropriate, general anesthesia with inhalational induction, and establishment of intravenous access. Airway should be controlled with an endotracheal tube. Atropine should be given for prophylaxis of the oculocardiac reflex and medications such as ondansetron should be given for nausea/vomiting prophylaxis.

What do I need to know about the surgical technique to optimize my anesthetic care?

Manipulation of the extraocular muscles can lead to bradycardia and arrhythmias via the oculocardiac reflex. Pretreatment with atropine is the best way to avoid this.

What can I do intraoperatively to assist the surgeon and optimize patient care?

Ensure adequate ventilation and oxygenation as well as adequate anesthetic depth. All of these maneuvers can help prevent the oculocardiac reflex. If the patient becomes bradycardia or has a dysrhythmia related to the oculocardiac reflex, inform the surgeon and instruct them to discontinue the manipulation of the eye until an anticholinergic medicine can be given and anesthetic depth increased. With repeat manipulation, the oculocardiac reflex often fatigues.

a. Neurologic:

N/A

b. If the patient is intubated, are there any special criteria for extubation?

Not specific to strabismus repair. Presence of difficult airway may lead to more cautious extubation.

c. Postoperative management

What analgesic modalities can I implement?

Acetaminophen suppository 30 mg/kg given at beginning of case then 10-20 mg/kg every 4-6 hours

What level bed acuity is appropriate?

Not applicable, usually ambulatory procedure.

What are common postoperative complications, and ways to prevent and treat them?

Incidence of postoperative nausea and vomiting is high (40-85%) and can delay discharge. Treatment should include prophylaxis with medication such as 5HT3 antagonist ondansetron (0.15 mg/kg IV) before manipulation of the eyes and adequate rehydration intraoperatively. Other medications and interventions such as gastric emptying can be considered. Parents should be informed of the high risk of nausea and vomiting associated with the surgery.

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